Aspect of T_{\text{c}} Enhancement and Face-Centered Cubic-Based A15 Structural Change in Cs3C60 Superconductors

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概要

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• With the recent experimental discovery of the superconducting transition temperature T_{\text{c}} = 38 K in Cs3C60 with an A15 structure under pressure, a generalized theory of the phonon-mediated electron--electron coupling in site representation formalism is developed to understand the superconducting mechanism from a unified picture of alkali-metal A-doped fullerenes. In this system with a large mass difference between A and C60, the roles of three kinds (acoustic, optical, intramolecular high-frequency) of phonons playing on T_{\text{c}} are analyzed for both face-centered cubic and body-centered cubic-based A15 structures. The essential point of the role of the structural difference in determining T_{\text{c}} is reflected by the existence of the optical phonon mode at tetrahedral (T) sites in the fcc structure, whether for promoting or preventing T_{\text{c}}. The ratio of optical phonon (V_{\text{o}}) coupling to higher frequency C60-tangential phonon (V_{\text{H}}) coupling with electrons contributing to superconductivity, i.e., V_{\text{o}}/V_{\text{H}}, changes the value of the contribution from 0.6 with promoting T_{\text{c}} in fcc to 0.16 with no effect on T_{\text{c}} in A15; however, a large density of states N(0) due to a one-dimensional electronic system is induced by A15-type superconductors. Furthermore, in Cs3C60, a theoretical aspect indicating that a common equation may be applied to the analysis of fullerene superconductivity regardless of structure, i.e., the fcc or A15-type structure, is discussed in comparison with recent experimental data of T_{\text{c}}, which is dependent on the volume per C60 ion.

• 2011-07-15

著者

• Matsushita Eiko

  Faculty Of Engineering Gifu University

• Kusaba Shin-ya

  Faculty of Engineering, Gifu University, Gifu 501-1193, Japan

• Matsushita Eiko

  Faculty of Engineering, Gifu University, Gifu 501-1193, Japan

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